This invention related to polymer films that are useful not only for detecting the presence of gaseous or liquid chemical substances but also for distinguishing one such chemical substance from another. In particular, the invention relates to polymer films that are capable of detecting gasoline vapor as distinguished from the vapor of diesel oil.
Providing automobiles with the wrong type of fuel is a common occurrence at gas stations. To prevent such accidents, the development of a new fuel detection system is strongly needed.
Conventional detectors of automotive fuels and other hydrocarbons are operated by either electrical or optical methods. An example of the electrical approach relies upon the adsorption of a substance to be detected on a semiconductor material, which causes a change in the resistance or conductance of the substance of interest. See, for example, Japanese Laid-Open Patent Application No. 74485/1975, which disclosed a gas detector that has two opposing electrodes provided on an insulating substrate, with a conductive powder containing a silicone rubber resistor being applied between the electrodes. Similar detectors are discloses in Japanese Laid-Open Patent Application Nos. 96846/1991 and 96847/1991, as well as German Laid-Open Patent Application No. 2,419,069 published Nov. 6, 1975. Brown et al. reported a method in which the change in the ion conductivity of a solid electrolyte (ion-exchange membrane) on account of gas adsorption is detected by polarography [See Proceedings of the Joint Conference on Sensing of Environmental Pollutants, AIAA Paper No. 71-1114, 1-3(1971)]. A similar method is disclosed in British Patent Publication No. 2,185,579 A2. However, these methods have two problems in common: first, temperature control is indispensable for reliable detection and, secondly, the monitoring of temperature control requires complicated equipment.
Japanese Laid-Open Patent Application No. 285439/1988 discloses a sensor that detects the leakage of hydrocarbons on the basis of the change in the impedance of a coaxial cable.
These sensors which detect hydrocarbons electrically have an inherent problem in that they are prone to operate incorrectly in the presence of disturbances such as induction noise and that the hydrocarbons to be detected have the potential to explode if they catch fire due to a spark or some other phenomena.
An example of the optical approach is described in Japanese Laid-Open Patent Application No. 156838/1980, which discloses a method of detecting the presence of an oil or the like on the basis of a change in the refractive index of a porous material that occurs when it absorbs an oil or the like. A similar method that relief upon fiber optics using capillarity is disclosed in European Patent Publication No. 0,282,009 A2. Japanese Laid-Open Patent Application No. 238746/1985 discloses an apparatus that has an infrared detector on the inner surface of the side wall of a hydrocarbon gas conducting duct to detect the concentration of a hydrocarbon gas of interest on the basis of the change in the absorbance of infrared light. Laid-Open Japanese Patent Application No. 47531/1987 discloses a sensor that relies upon a shift from the propagation mode in an optical fiber to the leakage mode that occurs as a result of oil or water deposition on the inner surface of the fiber.
The conventional hydrocarbon detectors described above, whether they adopt the electrical or optical approach, are capable of detecting the presence of hydrocarbons but it is difficult for them to detect a plurality of hydrocarbons as distinguished from each other. In particular, it is extremely difficult to detect gasoline as distinguished from diesel oil which has very similar properties to gasoline. As a further problem, hydrocarbons have the danger of catching fire but none of the detectors available today are designed to assure utmost safety in this regard. In addition, these detectors are not only bulky but also expensive.